In many sports the ability of an athlete to control the movement of his limbs is the key to his success. For example, in the sport of bowling, it is imperative that the bowler keep his arm straight and elbow locked during the delivery of the ball and follow-through after release. Even a slight bending of the elbow at this critical time will cause the ball to stray from the target. Many bowlers unconsciously, or as a result of a distraction, bend their arms during delivery of the ball causing missed shots and poor games. Athletes in other sports (e.g. golf, swimming, etc.) suffer similar mishaps due to an inability to keep a limb straight at the critical time.
It would be desirable to have a device which permitted an athlete to bend his arm or leg at will, but which would, at a critical time, lock the limb in a fully extended, straight position.